This invention relates to inkjet printers and, more particularly, to a monolithic printhead for an inkjet printer.
Inkjet printers typically have a printhead mounted on a carriage that scans back and forth across the width of a sheet of paper feeding through the printer. Ink from an ink reservoir, either on-board the carriage or external to the carriage, is fed to ink ejection chambers on the printhead. Each ink ejection chamber contains an ink ejection element, such as a heater resistor or a piezoelectric element, which is independently addressable. Energizing an ink ejection element causes a droplet of ink to be ejected through a nozzle for creating a small dot on the medium. The pattern of dots created forms an image or text.
As dot resolutions (dots per inch) increase along with the firing frequencies, more heat is generated by the firing elements. This heat needs to be dissipated. Heat is dissipated by a combination of the ink being ejected and the printhead substrate sinking heat from the ink ejection elements. The substrate may even be cooled by the supply of ink flowing to the printhead.
Additional information regarding one particular type of printhead and inkjet printer is found in U.S. Pat. No. 5,648,806, entitled, xe2x80x9cStable Substrate Structure For A Wide Swath Nozzle Array In A High Resolution Inkjet Printer,xe2x80x9d by Steven Steinfield et al., assigned to the present assignee and incorporated herein by reference.
As the resolutions and printing speeds of printheads increase to meet the demanding needs of the consumer market, new printhead manufacturing techniques and structures are required. Hence, there is a need for an improved printhead that has at least the following properties: adequately sinks heat from the ink ejection elements at high operating frequencies; provides an adequate refill speed of the ink ejection chambers with minimum blowback; minimizes cross-talk between nearby ink ejection chambers; is tolerant to particles within the ink; provides a high printing resolution; enables precise alignment of the nozzles and ink ejection chambers; provides a precise and predictable drop trajectory; is relatively easy and inexpensive to manufacture; and is reliable.
Described herein is a monolithic printhead formed using integrated circuit techniques. Thin film layers, including a resistive layer, are formed on a top surface of a silicon substrate. The various layers are etched to provide conductive leads to the heater resistor elements. Piezoelectric elements may be used instead of the resistive elements. An optional thermally conductive layer below the heater resistors sinks heat from the heater resistors and transfers the heat to a combination of the silicon substrate and the ink.
At least one ink feed hole is formed through the thin film layers for each ink ejection chamber.
A trench is etched in the bottom surface of the substrate so that ink can flow into the trench and into each ink ejection chamber through the ink feed holes formed in the thin film layers.
An orifice layer is formed on the top surface of the thin film layers to define the nozzles and ink ejection chambers. In one embodiment, a photodefinable epoxy is used to form the orifice layer.
A phosphosilicate glass (PSG) layer, providing an insulation layer beneath the resistive layer, is etched back from the ink feed holes and is protected by a passivation layer to prevent the ink from interacting with the PSG layer. Other layers may be protected from ink by being etched back in a similiar manner.
Various thin film structures are described as well as various ink feed arrangements and orifice layers.
The resulting fully integrated thermal inkjet printhead can be manufactured to a very precise tolerance since the entire structure is monolithic, meeting the needs for the next generation of printheads.